Trying to dissolve edge, but sometimes blender brings the origin to a face instead and doesn't dissolve the face. REALLY annoying!
I think you are confused about how to use  dissolve..  or about the differences between dissolve and delete:

check this fast video I made for you:

https://www.youtube.com/watch?v=7vEnOqUZ7Lk



also check:

Differences between dissolve and delete?

and this: